They are the most virulent and notoriously aggressive trees in the English landscape," said a man in Neighbours from Hell (ITV). He was talking about Cupressus Leylandii, a rapid-growth conifer and his remarks struck you initially as being a trifle overheated (in a horror film he would be the man who staggered into the pub, resin-streaked and croaking "The trees, beware the trees" - only to be laughed at by the regulars). But then you were shown Brenda and John Laws' cottage, a rural bungalow which used to have breathtaking views of the local countryside. The views still take the breath away, but they now also induce high blood pressure and, I should imagine, violent fantasies involving a chainsaw and the Laws' neighbour, Mr Foley. Because Mr Foley has planted a hedge of the devil trees just eight feet from the Laws' windows and, as a result, they might as well live in a hole in the ground. "You can feel the evil in them," said Mrs Laws about her oppressive hedge, and she is not alone. Rod Williams's film (an unembarrassed second bite at a subject that has already been covered by Cutting Edge and Modern Times) began with a Leylandii support group, the victims meeting to exchange snapshots of their evergreen tormentors.

Mr Foley didn't choose to defend his planting scheme, appearing only in those grainy long-lens stills that offer a visual shorthand for the presumption of guilt. The information that he had offered to buy the Laws' home at well under its market value suggested one motive for his deed, but in the absence of his voice you couldn't tell exactly what had seeded the spiteful enclosure in the first place. The other case histories suggested that there was always some provoking sin - imaginary or otherwise - which then swelled horribly into a buboe of mutual hatred. And the cruellest effect of such torments is that they turn the victims into the sort of obsessives that you wouldn't greatly care to live next to either - such as the distracted character who spent much of his spare time videoing his neighbour's cockerel ("It's just a natural thing - it's not a noise is it?" said the owner, as the bird did an imitation of corrugated-iron sheeting being hit with a golf club). Another long-suffering couple came out to gloat over the eviction of the woman next door, a whining drudge who appeared to have alienated the entire estate, to judge from the celebratory welcome for the bailiffs.

Sometimes the disputes were just toxic forms of social envy - as in the case of Marjorie and Raymond, whose conspicuous bid for status (Ladro ornaments, koi carp, Austrian blinds, PVC conservatory) had aroused the ire of neighbours on both sides. All parties denied envy in terms which only confirmed that comparison ruled their lives: "Fer a start, I've got a lot more garden than them," said one. "We drive about in a 1972 Rover. He drives about in a D-reg Escort that's dropping to bits," replied the other triumphantly. This was Ayckbourn on a dark day but the case of Mal Hussain, who lives a life under siege on a Lancaster council estate, was something infinitely more malevolent - a vision of the mob cruelty that can emerge when the law retreats and leaves a little fertile ground for hate to grow. The account of his purgatorial life rounded off easily the most depressing film broadcast for months.

With their series Secret Lives and Secret History, Channel 4 has been energetically establishing new definitions for the word "secret"; "Common knowledge but juicy enough to tell again," for instance, or "Everybody suspected but now we've got the pictures". Last night they added "Recently seen on the BBC" to the list, because Susan Steinberg's elegant film, Gold Fever, about the Klondike gold rush was strongly reminiscent of Jonathan Gili's recent film for Timewatch on exactly the same subject. There was a time when Channel 4 used to mutter bitterly about their broadcast neighbour's "copycat scheduling". Now it looks as if they are responding in kind. One can only hope it doesn't get out of hand, for the viewer's sake, if nobody else's.